Nice going there dude! Great job on the placements that give those amazing results. Kudos!! (Redundancy, I know
And please, not to ruffle any feathers (I think we've covered this before), the ALEXA add-on only tracks usage of those surfers who have added it on to their browsers. They do this by monitoring all your web activity. at times I've added it to my browser in the office when I want to see how we stack up to the competition., then promptly remove it. There's just something about having them track every single move I make on the web that I find a little unsettling.
All that said, it still most likely provides a representative view of visibility and comparison as there is no reason to think that ALEXA users surf any differently.
Whatever you are doing, keep it up, it obviously works!